The background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
All publications and patent applications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
Atropine is the tropine ester of tropic acid and is generally available as the sulfate salt. Nonenzymatic spontaneous hydrolysis of aqueous atropine yields tropine and tropic acid that are nontoxic but do not have biological activity in ophthalmic use. Stability has been tested, for example, for certain injectable formulations and degradation was observed over time for in-date and out-of-date formulations (Acad Emerg Med April 2004, Vol. 11, No. 4:329-334). Notably, atropine loss was significant in most cases, but less than 25% of the starting concentration. However, these formulations included atropine at high concentrations between 0.4 mg/ml and 2 mg/ml and had a very low pH (typically equal or less than pH4), which is in most cases unsuitable for ophthalmic use.
In ophthalmic use, atropine is marketed as Atropine Care (Akorn) formulated as a 1% drug solution for treatment of amblyopia and further contains 0.01% w/w of the preservative benzalkonium chloride. In another indication, atropine has also been used in several pediatric studies to slow down the progression of myopia. More specifically, children who received topically administered atropine drops had a slower disease progression than a control group in the same study. Advantageously, children receiving eye drops containing low atropine concentrations (e.g., in the range of 0.01-0.05%% w/v (0.01% w/w)) had significantly less photophobia and other side effects (see e.g., Ophthalmology, 2015:1-9). Indeed, the use of low-dose (i.e., 0.01%) atropine has become a preferred treatment of choice in slowing the progression of myopia. Unfortunately, the toxic effects of benzalkonium chloride have been demonstrated in the lab and in the clinic, and include tear film instability, loss of goblet cells, conjunctival squamous metaplasia and apoptosis, disruption of the corneal epithelium barrier, and damage to deeper ocular tissues (see e.g., Prog Retin Eye Res. 2010 Jul. 29(4):312-34).
In still further known compositions and methods, atropine formulations are described in WO 2017/204262 that include various buffer ingredients and water soluble polymers in which most formulations had a pH of about 4.3, 4.5, or 5.0 at an atropine concentration of 0.01% w/w. While such formulations were shown to reduce progression of myopia without exacerbating mydriatic action of atropine, stability of atropine as measured by an increase in tropic acid was less than desirable within as little as four weeks.
As normal tears have a pH of about 7.4, an ophthalmic solution should have the same pH as the lacrimal fluid. However, this is a challenge for an ophthalmic solutions containing atropine sulfate, as atropine sulfate is subjected to a greater degree of hydrolysis in solutions that are closer to neutral and basic pH conditions. Thus, atropine is more stable in ophthalmic solutions with a more acidic pH. For example, Atropine Care with a 1% w/w concentration of atropine is maintained at pH 5.5, but the shelf life is still limited to 15 months. Moreover, the degradation of atropine to tropic acid in aqueous solution is notably accelerated with reduced concentrations of atropine (e.g., U.S. Pat. No. 9,421,199), which still further compounds stability issues, particularly in low-dose atropine formulations.
To reduce hydrolytic degradation, water in low-dose atropine formulations can be at least in part replaced with deuterated (heavy) water as is described in the U.S. Pat. No. 9,421,199. While conceptually attractive to use kinetic isotope effects in stability, various disadvantages nevertheless remain. Among other things, at least some of the formulations of the '199 patent still contained a preservative. Moreover, deuterated water is still known to be subject to H/D exchange, and as such delivers deuterium to a subject receiving such formulations.
Alternatively, atropine may also be delivered at reduced concentrations from a cross-linked non-degradable polymer matrix as is described in US 2016/0338947. Unfortunately, to maintain the polymer away from the cornea, a shaped implant must be worn on the sclera that is typically not well tolerated or may produce discomfort.
Therefore, there is a need for improved storage stable ready-to-use compositions that contain atropine at low concentrations, have a physiologically desirable pH, and preferably do not contain a preservative.